Sharing channels in a licensed-assisted access in long term evolution operation

ABSTRACT

A channel sharing method includes determining a starting time for transmission on an LAA-LTE channel. A length of a hybrid preamble is determined based on the starting time and a predetermined transmission time boundary. Subsequent to determining the length of the hybrid preamble, the hybrid preamble having the determined length is transmitted. Subsequent to the hybrid preamble, a Long Term Evolution (LTE) signal is transmitted.

TECHNICAL FIELD

This disclosure relates to data transmission in communication systemsand, more specifically, to sharing channels in a licensed-assistedaccess in a Long Term Evolution (LAA-LTE) operation.

BACKGROUND

Operators have been looking at a number of ways to address the spectrumshortage issue and are increasingly looking towards the use ofunlicensed spectrum as a solution. In some implementations, a Long TermEvolution (LTE) air-interface can be used in unlicensed spectrum. Thegeneral technology variant of LTE that can be used in unlicensedspectrum is referred to as licensed-assisted access in LTE (LAA-LTE). Insome cases, LAA-LTE can use a licensed carrier as a primary cell (PCell)and an unlicensed carrier as a secondary cell (SCell). In some cases,cross-carrier scheduling can be used to schedule transmission on theunlicensed carrier. In a licensed-assisted operation, a transmissiongrant for a transmission on the unlicensed carrier can be transmitted onthe licensed carrier.

DESCRIPTION OF DRAWINGS

FIG. 1 is an example wireless communication system that shares a channelin an LAA-LTE operation.

FIG. 2 is an example timing diagram illustrating a first hybrid preamblestructure.

FIG. 3 is an example timing diagram illustrating a length indicationusing a Signaling Field (L-SIG) in the first hybrid preamble structure.

FIG. 4 is an example timing diagram illustrating a length indicationusing a Clear to Send (CTS) message in the first hybrid preamblestructure.

FIG. 5 is an example timing diagram illustrating a first hybrid preamblestructure without a Variable Length Section (VLS).

FIG. 6 is an example timing diagram illustrating a first hybrid preamblestructure without a Wireless Local Area Network (WLAN) CompatibleSection (WCS).

FIG. 7 is an example timing diagram illustrating an extended firsthybrid preamble structure.

FIG. 8 is an example timing diagram illustrating a second hybridpreamble structure.

FIG. 9 is an example timing diagram illustrating a length indicationusing a Signaling Field (L-SIG) in the second hybrid preamble structure.

FIG. 10 is an example timing diagram illustrating a length indicationusing a Clear to Send (CTS) message in the second hybrid preamblestructure.

FIG. 11 is an example timing diagram illustrating a second hybridpreamble structure without a Variable Length Section (VLS).

FIG. 12 is an example timing diagram illustrating a second hybridpreamble structure without a Wireless Local Area Network (WLAN)Compatible Section (WCS).

FIG. 13 is an example timing diagram illustrating an extended secondhybrid preamble structure.

FIG. 14 is an example timing diagram illustrating a Downlink (DL) hybridpreamble structure in a Load Based Equipment (LBE) operation.

FIG. 15 is an example timing diagram illustrating a Downlink (DL) hybridpreamble structure in a Frame Based Equipment (FBE) operation.

FIG. 16 is an example timing diagram illustrating a hybrid preamblestructure in a Downlink (DL) punctured LTE subframe.

FIG. 17 is an example timing diagram illustrating a hybrid preamblestructure with configurable transmission power.

FIG. 18 is an example timing diagram illustrating an Uplink (UL) hybridpreamble structure.

FIG. 19 is an example timing diagram illustrating a hybrid preamblestructure in a Time Division Multiplex (TDD) operation.

FIG. 20 is an example timing diagram illustrating a hybrid preamblestructure in an Uplink (UL) punctured LTE subframe.

FIG. 21 is a flowchart illustrating an example method for sharing achannel in an LAA-LTE operation.

FIG. 22 is a block diagram illustrating an example user equipment (UE)device.

FIG. 23 is a block diagram illustrating an example evolved Node B (eNB)device.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The present disclosure is directed to sharing channels in alicensed-assisted access in a Long Term Evolution (LAA-LTE) operation.An LAA-LTE operation can include a licensed carrier as a primary cell(PCell) and an unlicensed carrier as a secondary cell (SCell). In somecases, the unlicensed carrier in an LAA-LTE operation may be shared by aUser Equipment (UE) that operates on LAA-LTE technology and WirelessLocal Access Network (WLAN) devices that operate on WLAN technology. Inone example, the WLAN technology may include an 802.11 air interface. Insome cases, the WLAN devices may not recognize the waveform of a LongTerm Evolution (LTE) signal that is transmitted on the unlicensedcarrier. Therefore, the WLAN devices may treat the LTE signal as anunknown transmission. In some cases, the WLAN devices may be lesssensitive in detecting unknown transmissions. Thus, the WLAN devices mayattempt concurrent transmissions with the LTE signal on the unlicensedcarrier, and thereby create higher chances of interference or crosstalkon the LTE signal. In addition, because the WLAN devices may notrecognize the waveforms of the LTE signal, they may continue to monitorthe unlicensed carrier until the completion of the LTE signal, andtherefore increase power consumption of the WLAN devices.

Furthermore, in an LAA-LTE operation, the physical layer structure andframe format of the Long Term Evolution (LTE) air interface may be usedto enable forward migration from LTE systems. This approach enables anLAA-LTE system to include many LTE features, e.g., Orthogonal FrequencyDivision Multiple Access (OFDMA), frequency domain scheduling, andcross-carrier scheduling.

In some implementations, a WLAN device may transmit a WLAN preambleprior to transmitting a WLAN signal on the unlicensed carrier. The WLANpreamble may indicate the length of the WLAN signal. Other WLAN devicesmay detect the WLAN preamble and determine the length of the WLAN signalaccordingly. Other WLAN devices may thus save their battery power bystopping monitoring the unlicensed carrier and turning off part of theircircuit components until the WLAN signal is transmitted. However, WLANtransmissions may not be compatible with the LTE frame structure becausethe WLAN operates on asynchronous channel access. For example, the WLANpreamble and the subsequent WLAN signal may be transmitted as soon asthe unlicensed carrier is available. In contrast, the LTE framestructure, which supports both Frequency Division Duplex (FDD) and TimeDivision Duplex (TDD) operations, operates on a synchronous framestructure. Therefore, an LTE signal in an LAA-LTE operation may betransmitted on the unlicensed carrier at fixed transmission timeboundaries. These fixed boundaries can be referred to as theTransmission Time Interval (TTI) boundaries. When an LAA-LTE equipmentsuch as an eNB or a UE wants to transmit on an unlicensed carrier, theLAA-LTE equipment determines whether the channel is available fortransmission (e.g. by listening to the channel and determining that thechannel is unoccupied). However, at an instant when the unlicensedcarrier is available to carry an LTE signal the UE or the eNB may not beable or permitted to transmit an LTE signal because the LTE signaltransmission are specified to start at TTI boundaries and the instantfor transmission on the unlicensed carrier does not coincide with a TTIboundary.

In some implementations, hybrid preambles may be used to share channelsin an LAA-LTE operation. A hybrid preamble may indicate the length of anLTE signal that is transmitted on the unlicensed carrier, whilemaintaining compatibility with the LTE frame structure.

FIG. 1 is an example wireless communication system 100 that shareschannels in a licensed-assisted access in Long Term Evolution (LAA-LTE)operation. For example, in a wireless communication system, a startingtime for transmission on an LAA-LTE channel may be determined. In someimplementations, the LAA-LTE channel is an unlicensed carrier that isconfigured for a licensed-assisted operation. In some cases, thedetermination may be performed by an evolved Node B (eNB) prior to aDownlink (DL) transmission by the eNB. Alternatively or in combination,the determination may be performed by a User Equipment (UE) prior to anUplink (UL) transmission by the UE. A length of a hybrid preamble may bedetermined based on the starting time and a predetermined transmissiontime boundary. In some cases, the predetermined transmission timeboundary is a Transmission Time Interval (TTI) boundary.

In some cases, the hybrid preamble may include a Wireless Local AreaNetwork (WLAN) Compatible Section (WCS) that indicates a length of theLTE signal. In these cases, the length of the hybrid preamble may beequal to the duration of the Wireless Local Area Network (WLAN)Compatible Section (WCS). In some cases, the hybrid preamble may includea Wireless Local Area Network (WLAN) Compatible Section (WCS) and aVariable Length Section (VLS). The WCS may indicate a length of the LTEsignal. The VLS may have a length that is determined based on adifference between the length of the hybrid preamble and a length of theWCS. In these cases, the length of the hybrid preamble may be largerthan the length of the WCS. In some cases, the hybrid preamble includesa Variable Length Section (VLS) having a length that is determined basedon the length of the hybrid preamble.

Subsequent to the determination of the length of the hybrid preamble,the hybrid preamble having the determined length may be transmitted. Insome cases, the transmission may be a DL transmission that istransmitted by the eNB. Alternatively or in combination, thetransmission may be a UL transmission that is transmitted by the UE. Insome cases, prior to transmitting the hybrid preamble, a transmissiongrant that grants a transmission of the LTE signal and an indicationthat indicates a transmission power level of the hybrid preamble may bereceived. The indication may indicate that the hybrid preamble istransmitted at a normal power level or at a reduced power level. Inthese cases, the hybrid preamble may be transmitted in accordance withthe indication.

In some implementations, the hybrid preamble is transmitted in a firstsubframe prior to the predetermined transmission time boundary, and theLTE signal is transmitted in a second subframe after the predeterminedtransmission time boundary. In some cases, the first subframe where thehybrid preamble is transmitted includes an LTE signal adapted to occupyonly a subset of symbols in the first subframe. In these cases, thehybrid preamble is transmitted during a time period corresponding tosymbols not within the subset. In some cases, the subset of symbols thatare occupied in the first subframe are at the beginning of the subframe.In some other cases, the subset of the symbols that are occupied in thefirst subframe are at the end of the subframe.

Subsequent to the hybrid preamble, a Long Term Evolution (LTE) signalmay be transmitted. In some implementations, a transmission grant thatgrants a transmission of a different LTE signal may be received. Thetransmission grant may include an indication to transmit the second LTEsignal without a preceding hybrid preamble. In response to theindication, the second LTE signal may be transmitted without a precedinghybrid preamble.

Sharing a channel in an LAA-LTE operation according to methods andsystems described herein may for example, enable WLAN devices via thehybrid preamble to detect LTE transmissions on an LAA-LTE channel anddetermine the length of the LTE transmissions. This approach enables theWLAN devices to save power because they can turn off part of theirreceiver circuit components until the LTE transmissions are completed.This approach may also mitigate interferences generated by WLAN devicesduring the LTE transmissions as the hybrid preamble can be detected bythe WLAN devices at a lower signal level because of the presence of theknown WLAN preambles in the hybrid preamble. Furthermore, this approachprovides a hybrid preamble that is compatible to the existing LTE framestructure for both FDD and TDD operations. Therefore, the LAA-LTEoperation can the reuse LTE features, such as Orthogonal FrequencyDivision Multiple Access (OFDMA) and cross-carrier scheduling.

At a high level, the example wireless communication system 100 includesa UE 102 and a wireless communication network 110, which includes an eNB104 that is configured to communicate with the UE 102. In theillustrated example, the UE 102 may transmit an LTE signal to the eNB104 on the LAA-LTE channel 120 in a UL transmission. The eNB 104 maytransmit an LTE signal to the UE 102 on the LAA-LTE channel 120 in a DLtransmission. In some instances, the LAA-LTE channel 120 may be anunlicensed carrier.

In a UL transmission, the UE 102 determines a starting time fortransmitting on an LAA-LTE channel. The UE 102 determines a length of ahybrid preamble (to be transmitted by the UE before transmission of anLTE signal to the eNB) based on the starting time and a TransmissionTime Interval (TTI) boundary. The UE 102 transmits, subsequent todetermining the length of the hybrid preamble, the hybrid preamblehaving the determined length. Subsequent to the hybrid preamble, the UE102 transmits a Long Term Evolution (LTE) signal.

In a DL transmission, the eNB 104 determines a starting time fortransmitting on an LAA-LTE channel. The eNB 104 determines a length of ahybrid preamble (to be transmitted by the eNB before transmission of anLTE signal to the UE) based on the starting time and a Transmission TimeInterval (TTI) boundary. The eNB 104 transmits, subsequent todetermining the length of the hybrid preamble, the hybrid preamblehaving the determined length. Subsequent to the hybrid preamble, the eNB104 transmits a Long Term Evolution (LTE) signal. FIGS. 2-23 andassociated descriptions provide additional details of both UL and DLtransmissions.

Turning to a general description of the elements, a UE may be referredto as mobile electronic device, user device, mobile station, subscriberstation, portable electronic device, mobile communications device,wireless modem, or wireless terminal. Examples of a UE (e.g., the UE102) may include a cellular phone, personal data assistant (PDA), smartphone, laptop, tablet personal computer (PC), pager, portable computer,portable gaming device, wearable electronic device, or other mobilecommunications device having components for communicating voice or datavia a wireless communication network. The wireless communication networkmay include a wireless link over at least one of a licensed spectrum andan unlicensed spectrum.

Other examples of a UE include mobile and fixed electronic device. A UEmay include a Mobile Equipment (ME) device and a removable memorymodule, such as a Universal Integrated Circuit Card (UICC) that includesa Subscriber Identity Module (SIM) application, a Universal SubscriberIdentity Module (USIM) application, or a Removable User Identity Module(R-UIM) application. The term “UE” can also refer to any hardware orsoftware component that can terminate a communication session for auser. In addition, the terms “user equipment,” “UE,” “user equipmentdevice,” “user agent,” “UA,” “user device,” and “mobile device” can beused synonymously herein.

The wireless communication network 110 may include one or a plurality ofradio access networks (RANs), core networks (CNs), and externalnetworks. The RANs may comprise one or more radio access technologies.In some implementations, the radio access technologies may be GlobalSystem for Mobile communication (GSM), Interim Standard 95 (IS-95),Universal Mobile Telecommunications System (UMTS), CDMA2000 (CodeDivision Multiple Access), Evolved Universal Mobile TelecommunicationsSystem (UMTS), Long Term Evaluation (LTE), or LTE-Advanced. In someinstances, the core networks may be evolved packet cores (EPCs).

A RAN is part of a wireless telecommunication system which implements aradio access technology, such as UMTS, CDMA2000, 3GPP LTE, and 3GPPLTE-A. In many applications, a RAN includes at least one eNB 104. An eNB104 may be a radio base station that may control all or at least someradio-related functions in a fixed part of the system. The eNB 104 mayprovide radio interface within their coverage area or a cell for the UE102 to communicate. The eNB 104 may be distributed throughout thecellular network to provide a wide area of coverage. The eNB 104directly communicates to one or a plurality of UEs, other base stations,and one or more core network nodes.

While described in terms of FIG. 1, the present disclosure is notlimited to such an environment. The eNB 104 may operate on any of thedifferent wireless communication technologies. Example wirelesstechnologies include Global System for Mobile Communication (GSM),Universal Mobile Telecommunications System (UMTS), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), wireless broadband communicationtechnologies, and others. Example wireless broadband communicationsystem includes IEEE 802.11 wireless local area network, IEEE 802.16WiMAX network, and others.

While elements of FIG. 1 are shown in FIGS. 22 and 23 as includingvarious component parts, portions or modules that implement the variousfeatures and functionality, nevertheless these elements may insteadinclude a number of sub-modules, third-party services, components,libraries, and such, as appropriate. Furthermore, the features andfunctionality of various components can be combined into fewercomponents as appropriate.

FIG. 2 is an example timing diagram 200 illustrating a first hybridpreamble structure. The example timing diagram 200 includes a hybridpreamble 210 and an LTE signal 206. The hybrid preamble 210 begins at astarting time 220, which is the time at which the transmitting entity,e.g., the UE for UL or the eNB for DL, determines that transmission onthe unlicensed carrier is allowed. In operation, WLAN devices may detectthe transmission of the hybrid preamble 210 and recognize that thechannel is occupied. The hybrid preamble 210 ends at a TTI boundary 222.The LTE signal 206 begins after transmission of the hybrid preamble 210at the TTI boundary 222. Therefore, the transmission of the LTE signal206 is compatible with the LTE frame structure.

In the illustrated example, the hybrid preamble 210 includes a VariableLength Section (VLS) 202 and a WLAN Compatible Section (WCS) 204. In theillustrated example, the VLS 202 is transmitted prior to the WCS 204although the VLS and WCS may be reversed as will be describedhereinafter. The WCS 204 may be formatted in accordance with signalstransmitted by WLAN devices and, therefore, the WCS 204 may be detectedand decoded by WLAN devices. The WCS 204 may include an indication ofthe duration of the LTE signal which is to be transmitted following thehybrid preamble 210. Therefore, the WLAN devices may be informed of orotherwise determine the length of time for which the channel will beoccupied and turn off their circuits to save battery power.

In some implementations, the WCS 204 has a length that is specifiedaccording to WLAN technologies. This length is denoted as T_(wcs) in theillustrated example. The length of the hybrid preamble 210 is denoted asT_(HP), which begins at the starting time 220 and ends at the TTIboundary 222. In the illustrated example, the length of the hybridpreamble 210 is greater than the length of the WCS 204, and therefore, aVLS, i.e., the VLS 202, is included in the hybrid preamble 210. The VLS202 may be used to occupy the channel. In some cases, the starting time220 may occur at any time, while the TTI boundary 222 occurs at a fixedtime boundary. Therefore, the length of the hybrid preamble 210 mayvary. Because the length of the WCS 204 is fixed, the length of the VLS202, denoted as T_(VLS), may also vary. In some cases, the length of theVLS 202 may be the difference of the length of the hybrid preamble 210and the length of the WCS 204. In some cases, the length of the VLS 202may be reduced by the length of any gap in transmission in the VLS 202.The gap may be small enough so that WLAN devices may not occupy themedium during the gap. For example, the gap may be less than a ShortInter Frame Spacing (SIFS) in WLAN technologies. In some case, the SIFSmay be about 10 μsec for 802.11n at 2.5 GHz, or about 16 μsec for802.11a and 802.11c. This approach may simplify implementation of thetransmitter when transitioning between the VLS 202 and the WCS 204.Additionally, this approach may increase the probability that WLANdevices monitoring the channel may correctly decode the WCS 204 becausethe gap may function similarly to an idle period in a WLAN transmission.

In some cases, the VLS 202 may include a known preamble sequence.Examples of the known preamble sequence may include cell-specificreference signals in downlink, sounding reference signal sequence inuplink, WLAN-specific preambles such as Short Training Field (L-STF) orLong Training Field (L-LTF), or other preamble sequences. In some cases,the known preamble sequences may be repeated a number of times toconstruct the VLS of the desired length. Known preamble sectionsequences may be used by the receiving LAA-LTE devices for channelestimation purposes. In some implementations, a receiver may calculatethe length of the VLS based on the starting time of the VLS, the nextTTI boundary, and the length of the WCS.

FIG. 3 is an example timing diagram 300 illustrating a length indicationusing a Signaling Field (L-SIG) in the first hybrid preamble structure.The example timing diagram 300 includes a hybrid preamble 310 and an LTEsignal 306. The hybrid preamble 310 begins at a starting time 320, whichis the time at which the transmitting entity, e.g., the UE for UL or theeNB for DL, determines that transmission on the unlicensed carrier isallowed. In operation, WLAN devices may detect the transmission of thehybrid preamble 310 and recognize that the channel is occupied. Thehybrid preamble 310 ends at a first side of a TTI boundary 322. The LTEsignal 306 begins at another, adjacent side the TTI boundary 322.Therefore, the transmission of the LTE signal 306 is compatible with theLTE frame structure. In the illustrated example, the hybrid preamble 310includes a VLS 302 and a WCS 304. In the illustrated example, the VLS302 is transmitted prior to the WCS 304.

In the illustrated example, the WCS 304 includes an L-STF 312, an L-LTF314, and an L-SIG 316. The L-STF 312, the L-LTF 314, and the L-SIG 316are legacy fields that can be detected by WLAN devices. In someimplementations, the L-STF 312 and the L-LTF 314 are known preambles tosome WLAN devices, e.g., devices that operate on 802.11n technologies.In some implementations, WLAN devices can also detect the signal,perform frequency offset estimation, or timing synchronization bydetecting the L-STF 312 and the L-LTF 314. Because the L-STF 312 and theL-LTF 314 are known preambles to some WLAN devices, these WLAN devicesmay detect the transmission on the medium at a lower signal level. Insome instances, the L-SIG 316 may include information that indicates thelength of the LTE signal 306 which is to be transmitted after the hybridpreamble 310. In some implementations, the length of the LTE signal maybe fixed, e.g., specified in a standard. In some implementations, thelength of the LTE signal may be varied and determined by thetransmitting node (i.e., eNB in DL and UE in UL). Alternatively, thelength of the LTE signal may be determined by the eNB regardless of thedirection of transmission, i.e., for both DL and UL transmission andthis is signaled to the UE.

In some implementations, the L-SIG 316 can be set in bytes assumingtransmission at the rate of 6 Mbps. For example, the L-SIG 316 can beset based on the following equation:

L-SIG=n×[1 ms×6 mbps]=(n×750) bytes, where n indicates the number ofconsecutive TTI that may be included in the LTE signal 306.

In some cases, a maximum value of n (i.e. N_(max)) may be determinedbased on regulatory requirements.

FIG. 4 is an example timing diagram 400 illustrating a length indicationusing a Clear to Send (CTS) message in the first hybrid preamblestructure. The example timing diagram 400 includes a hybrid preamble 410and an LTE signal 406. The hybrid preamble 410 begins at a starting time420, which is the time at which the transmitting entity, e.g., the UEfor UL or the eNB for DL, determines that transmission on the unlicensedcarrier is allowed. In operation, WLAN devices may detect thetransmission of the hybrid preamble 410 and recognize that the channelis occupied. The hybrid preamble 410 ends at one side of a TTI boundary422. The LTE signal 406 begins at the other side of the TTI boundary422. Therefore, the transmission of the LTE signal 406 is compatiblewith the LTE frame structure. In the illustrated example, the hybridpreamble 410 includes a VLS 402 and a WCS 404. In the illustratedexample, the VLS 402 is transmitted prior to the WCS 404.

In the illustrated example, the WCS 404 includes a CTS message. A CTSmessage may include a duration that indicates the length of the LTEsignal 406 which is to be transmitted after the hybrid preamble 410. Theduration may be set in a similar manner as the L-SIG field. In someimplementations, WLAN devices may use the duration field in the CTSmessage to perform virtual carrier sensing mechanism and to update theNetwork Allocation Vector (NAV). The duration indicates that the mediumis likely to be busy during the period of time as indicated and,therefore, the WLAN devices may turn off part of their circuitcomponents until the end of the duration. In some implementations, theWCS 404 may include a Request to Send (RTS) message that also includes aduration field.

FIG. 5 is an example timing diagram 500 illustrating a first hybridpreamble structure without a Variable Length Section (VLS). Such ahybrid preamble may be constructed when a time to reach the TTI boundaryis substantially equal to a duration of the WCS. The example timingdiagram 500 includes a hybrid preamble 510 and an LTE signal 506. Thehybrid preamble 510 begins at a starting time 520, which is the time atwhich the transmitting entity, e.g., the UE for UL or the eNB for DL,determines that transmission on the unlicensed carrier is allowed. Inoperation, WLAN devices may detect the transmission of the hybridpreamble 510 and recognize that the channel is occupied. The hybridpreamble 510 ends at a TTI boundary 522. The LTE signal 506 begins atthe TTI boundary 522. Therefore, the transmission of the LTE signal 506is compatible with the LTE frame structure. In the illustrated example,the hybrid preamble 510 includes a WCS, but not a VLS. The length of thehybrid preamble 510 is equal to the fixed length of the WCS

FIG. 6 is an example timing diagram 600 illustrating a first hybridpreamble structure without a WCS. The example timing diagram 600includes a hybrid preamble 610 and an LTE signal 606. The hybridpreamble 610 begins at a starting time 620, which is the time at whichthe transmitting entity, e.g., the UE for UL or the eNB for DL,determines that transmission on the unlicensed carrier is allowed. Inoperation, WLAN devices may detect the transmission of the hybridpreamble 610 and recognize that the channel is occupied. The hybridpreamble 610 ends at a TTI boundary 622. The LTE signal 606 begins atthe TTI boundary 622. Therefore, the transmission of the LTE signal 606is compatible with the LTE frame structure. In the illustrated example,the length of the hybrid preamble 610 is smaller than the fixed lengthof a WCS. In the illustrated example, the hybrid preamble 610 includes aVLS, but not a WCS. In this case, the length of the VLS is the same asthe length of the hybrid preamble 610. This scenario may occur when thetransmitting entity determines that the fixed WCS cannot be included inthe hybrid preamble because the WCS has a longer duration in comparisonto a time between the next TTI boundary (622) and the current instant(620) that a transmission may commence. In one instance such a hybridpreamble may be constructed without WCS when, for example, thetransmitting entity wants to transmit an LTE signal without having towait for the next TTI boundary. Accordingly the hybrid preamble may betransmitted without WCS to reserve the channel by preventing WLAN devicefrom transmitting thereon since the VLS may include a knownWLAN-specific preamble such as Short Training Field (L-STF) or LongTraining Field (L-LTF), or other preamble sequences. Furthermore, theknown preamble sequences may be repeated a number of times to constructthe VLS of the desired length until the TTI boundary is reached.

FIG. 7 is an example timing diagram 700 illustrating an extended firsthybrid preamble structure. The example timing diagram 700 includes TTIboundaries 722, 724, and 726. The timing diagram 700 includes a clearchannel assessment (CCA) period 732, where the channel is sensed todetermine whether the channel is available for carrying a transmission.In some implementations, the channel may be sensed by the e.g., the eNBfor DL or the UE or UL. In some cases, the transmitting entity mayestimate the energy of the channel to sense whether the channel isavailable. The timing diagram 700 also includes a hybrid preamble 750and an LTE signal 706. The hybrid preamble 750 begins at a starting time742, when the channel is determined to be available for transmission. Inthe illustrated example, the time between the starting time 742 and thenext TTI boundary 724 is smaller than a duration of a WCS. In theillustrated example, the hybrid preamble 750 extends to the followingTTI boundary 726. In the illustrated example, the hybrid preamble 750includes a WCS 704 and a VLS 702. In the illustrated example, the VLS702 is transmitted prior to the WCS 704.

In some implementations, a second hybrid preamble structure may be used.In the second hybrid preamble structure, a WCS is transmitted before aVLS rather than vice-versa (i.e. VLS before WCS) as described withregard to FIGS. 2-7. FIGS. 8-13 and associated descriptions provideadditional details of these implementations.

FIG. 8 is an example timing diagram 800 illustrating a second hybridpreamble structure. The example timing diagram 800 includes a hybridpreamble 810 and an LTE signal 806. The hybrid preamble 810 begins at astarting time 820, which is the time at which the transmitting entity,e.g., the UE for UL or the eNB for DL, determines that transmission onthe unlicensed carrier is allowed. In operation, WLAN devices may detectthe transmission of the hybrid preamble 810 and recognize that thechannel is occupied. The hybrid preamble 810 ends at a TTI boundary 822.The LTE signal 806 begins at the TTI boundary 822. Therefore, thetransmission of the LTE signal 806 is compatible with the LTE framestructure. In the illustrated example, the hybrid preamble 810 includesa VLS 802 and a WCS 804. In the illustrated example, the VLS 802 istransmitted after the WCS 804. The WCS 804 may be formatted inaccordance with signals transmitted by WLAN devices and, therefore, theWCS 804 may be detected and decoded by WLAN devices. The WCS 804 mayinclude an indication of the duration of the LTE signal. Therefore, theWLAN devices may determine the length of time for which the channel willbe occupied and turn off their circuits to save battery power. Asdescribed previously, the length of the VLS 802 may be determined basedon the length of the hybrid preamble 810 and the length of the WCS 804.In some cases, the VLS 802 may include a known preamble sequence.

FIG. 9 is an example timing diagram 900 illustrating a length indicationusing a Signaling Field (L-SIG) in the second hybrid preamble structure.The example timing diagram 900 includes a hybrid preamble 910 and an LTEsignal 906. The hybrid preamble 910 begins at a starting time 920, whichis the time at which the transmitting entity, e.g., the UE for UL or theeNB for DL, determines that transmission on the unlicensed carrier isallowed. In operation, WLAN devices may detect the transmission of thehybrid preamble 910 and recognize that the channel is occupied. Thehybrid preamble 910 ends at a TTI boundary 922. The LTE signal 906begins at the TTI boundary 922. Therefore, the transmission of the LTEsignal 906 is compatible with the LTE frame structure. In theillustrated example, the hybrid preamble 910 includes a VLS 902 and aWCS 904. In the illustrated example, the VLS 902 is transmitted afterthe WCS 904. In the illustrated example, the WCS 904 includes an L-STF912, an L-LTF 914, and an L-SIG 916. In some implementations, the L-STF912 and the L-LTF 914 are known preambles to some WLAN devices. In someinstances, the L-SIG 916 may include information that indicates thelength of the LTE signal 906.

FIG. 10 is an example timing diagram 1000 illustrating a lengthindication using a using a Clear to Send (CTS) message in the secondhybrid preamble structure. The example timing diagram 1000 includes ahybrid preamble 1010 and an LTE signal 1006. The hybrid preamble 1010begins at a starting time 1020, which is the time at which thetransmitting entity, e.g., the UE for UL or the eNB for DL, determinesthat transmission on the unlicensed carrier is allowed. In operation,WLAN devices may detect the transmission of the hybrid preamble 1010 andrecognize that the channel is occupied. The hybrid preamble 1010 ends ata TTI boundary 1022. The LTE signal 1006 begins at the TTI boundary1022. Therefore, the transmission of the LTE signal 1006 is compatiblewith the LTE frame structure. In the illustrated example, the hybridpreamble 1010 includes a VLS 1002 and a WCS 1004. In the illustratedexample, the VLS 1002 is transmitted after the WCS 1004. In theillustrated example, the WCS 1004 includes a CTS message. A CTS messagemay include a duration that indicates the length of the LTE signal 1006.The duration may be set in a similar manner as the L-SIG field.

FIG. 11 is an example timing diagram 1100 illustrating a second hybridpreamble structure without a Variable Length Section (VLS). The exampletiming diagram 1100 includes a hybrid preamble 1110 and an LTE signal1106. The hybrid preamble 1110 begins at a starting time 1120, which isthe time at which the transmitting entity, e.g., the UE for UL or theeNB for DL, determines that transmission on the unlicensed carrier isallowed. In operation, WLAN devices may detect the transmission of thehybrid preamble 1110 and recognize that the channel is occupied. Thehybrid preamble 1110 ends at a TTI boundary 1122. The LTE signal 1106begins at the TTI boundary 1122. Therefore, the transmission of the LTEsignal 1106 is compatible with the LTE frame structure. In theillustrated example, the length of the hybrid preamble 1110 is equal tothe fixed length of a WCS. Therefore, the hybrid preamble 1110 includesa WCS, but not a VLS.

FIG. 12 is an example timing diagram 1200 illustrating a second hybridpreamble structure without a WCS. The example timing diagram 1200includes a hybrid preamble 1210 and an LTE signal 1206. The hybridpreamble 1210 begins at a starting time 1220, which is the time at whichthe transmitting entity, e.g., the UE for UL or the eNB for DL,determines that transmission on the unlicensed carrier is allowed. Inoperation, WLAN devices may detect the transmission of the hybridpreamble 1210 and recognize that the channel is occupied. The hybridpreamble 1210 ends at a TTI boundary 1222. The LTE signal 1206 begins atthe TTI boundary 1222. Therefore, the transmission of the LTE signal1206 is compatible with the LTE frame structure. In the illustratedexample, the length of the hybrid preamble 1210 is smaller than thefixed length of a WCS. In the illustrated example, the hybrid preamble1210 includes a VLS, but not a WCS. In this case, the length of the VLSis the same as the length of the hybrid preamble 1210.

FIG. 13 is an example timing diagram 1300 illustrating an extendedsecond hybrid preamble structure. The example timing diagram 1300includes TTI boundaries 1322, 1324, and 1326. The timing diagram 1300includes a clear channel assessment (CCA) period 1332, where channel issensed to determine whether the channel is available. The timing diagram1300 also includes a hybrid preamble 1350 and an LTE signal 1306. Thehybrid preamble 1310 begins at a starting time 1342, when the channel isavailable for access. In the illustrated example, the time between thestarting time 1342 and the next TTI boundary 1324 is smaller than aduration of a WCS. In the illustrated example, the hybrid preamble 1350extends to the following TTI boundary 1326. In the illustrated example,the hybrid preamble 1350 includes a WCS 1304 and a VLS 1302. In theillustrated example, the VLS 1302 is transmitted after the WCS 1304.

In general, a hybrid preamble comprises either a VLS or a WCS or both.When both VLS and WCS are included in the hybrid preamble, then they maybe transmitted in either order (i.e. WCS before VLS or VLS before WCS).The WCS may comprise any signal that is compatible with WLAN and mayinclude an indication of length of the LTE signal that follows the HP.The WCS may comprise a CTS or an RTS signal or a combination of L-STF,L-LTF and L-SIG fields. The transmitting node transmits the hybridpreamble until the TTI boundary is reached, followed by the LTE signal.FIG. 14 is an example timing diagram 1400 illustrating a Downlink (DL)hybrid preamble structure in a Load Based Equipment (LBE) operation. Theillustrated hybrid preamble may be used in either a TDD system or an FDDsystem. The timing diagram 1400 includes an LTE frame 1440, whichincludes a subframe 1442. The timing diagram 1400 also includes a CCAperiod 1432, a hybrid preamble 1410, and an LTE signal 1406. Inaddition, the timing diagram 1400 includes TTI boundaries 1422 and 1424.

In the illustrated example, the transmitter may use the subframe 1442for CCA and hybrid preamble transmission. In such a case, the subframe1442, which is the last subframe in the LTE frame 1440, may not be usedfor transmission in the LTE frame 1440. In the illustrated example, theCCA period 1432 begins at the TTI boundary 1422. In an LBE operation, adevice may perform a Clear Channel Assessment (CCA) check using “energydetect” before transmitting on an unlicensed carrier. In some cases, theCCA period 1432 may be more than 18 μs. The hybrid preamble 1410 beginsat a starting time 1420, when the channel is available for transmissionbased on CCA. The hybrid preamble 1410 ends on the TTI boundary 1424,where the LTE signal 1406 begins. In some cases, the LTE signal 1406 mayoccupy up to 10 ms based on regulatory requirements.

FIG. 15 is an example timing diagram 1500 illustrating a Downlink (DL)hybrid preamble structure in a Frame Based Equipment (FBE) operation.The illustrated hybrid preamble may be used in either a TDD system or anFDD system. The timing diagram 1500 includes an LTE frame 1540, whichincludes a slot 1542. The timing diagram 1500 also includes an idleperiod 1534, a CCA period 1532, a hybrid preamble 1510, and an LTEsignal 1506. In addition, the timing diagram 1400 includes TTI boundary1524.

In an FBE operation, a device may perform a Clear Channel Assessment(CCA) check using “energy detect” before transmitting on an unlicensedcarrier. The Channel Occupancy Time may be in the range of about 1 ms toabout 10 ms. An idle period may be included before the CCA. In somecases, the idle period may be at least 5% of the Channel Occupancy Timeused by the device for the current transmission period.

In the illustrated example, the eNB may use the slot 1542 for CCA andhybrid preamble transmission. In such a case, the eNB may not transmitDL LTE signal transmissions in the slot 1542, which is the last slot inthe LTE frame 1540. In the illustrated example, the idle period 1534begins at the TTI boundary prior to the slot 1542 (i.e. at the beginningof the slot preceding the slot 1542), followed by the CCA period 1532.In some cases, the CCA period 1532 may be more than about 18 μs. Thehybrid preamble 1510 begins at a starting time 1520, when the channel isavailable for transmission based on CCA. The hybrid preamble 1510 endson the TTI boundary 1524, where the LTE signal 1506 begins. In theillustrated example, the slot immediately prior to the slot 1542 is nottransmitted and is referred to as the idle period, i.e., in aDiscontinuous Transmission (DTX) mode.

FIG. 16 is an example timing diagram 1600 illustrating a hybrid preamblestructure in a Downlink (DL) punctured LTE subframe. The illustratedhybrid preamble may be used in either a TDD system or an FDD system. Thetiming diagram 1600 includes an LTE subframe 1640. The timing diagram1600 also includes an idle period 1634, a CCA period 1632, and a hybridpreamble 1610. In addition, the timing diagram 1600 includes an LTEsignal 1606 that begins at a TTI boundary 1624.

In the illustrated example, the LTE subframe 1640 may be punctured. Insome cases, one OFDM symbol in the LTE subframe 1640 is used for CCA andhybrid preamble transmission and, therefore, is not used for LTE signaltransmission. In these cases, the OFDM symbol is an untransmitted OFDMsymbol. In the illustrated example, the last OFDM symbol is theuntransmitted OFDM symbol in the LTE subframe 1640. In some cases, theuntransmitted OFDM symbol may be the first OFDM symbol in the LTEsubframe. In some cases, more than one OFDM symbols may beuntransmitted, and the untransmitted OFDM symbols may be located at anyposition within the LTE subframe. In some cases, the transmitter maytransmit the same amount of data in the punctured LTE subframe 1640 asother subframes in a transmission. In these cases, the code rate of theLTE subframe 1640 may be higher than other subframes. In the illustratedexample, the idle period 1634 begins where last OFDM symbol begins,followed by the CCA period 1632. In some cases, the duration of the idleperiod 1634 may be about 50 μs. In some cases, the CCA period 1632 maybe more than about 18 μs. The hybrid preamble 1610 begins at a startingtime 1620, when the channel is available for access based on CCA. Thehybrid preamble 1610 ends on the TTI boundary 1624, where the LTE signal1606 begins. In some implementations, e.g., in an LBE operation, theidle period 1634 may be omitted. This approach may reduce the overheadfor CCA and hybrid preamble transmission. In some cases, this approachmay be used when the eNB scheduler determines whether or not to accessthe channel on a per TTI basis.

FIG. 17 is an example timing diagram illustrating a hybrid preamblestructure with configurable transmission power. In some cases, the ULtransmission of the LAA-LTE channel may operate in scheduled mode. Forexample, an eNB may signal uplink grants for one or more of the UEs totransmit on a given subframe in the uplink of the unlicensed carrier.The grants may be sent on a separate paired downlink carrier operatingin either licensed or unlicensed spectrum, or on the same carrierfrequency in a TDD manner. Cross-carrier scheduling may be used, forexample where the scheduling is transmitted on a downlink carrier whichis paired with a different uplink carrier.

In general, a portion of the LTE frame structure may be left unused forLTE signal transmission. This is done to facilitate CCA and transmissionof hybrid preamble by the transmitter in these unused portions of theLTE frame structure. This portion of unused LTE frame structure may bean LTE slot or an LTE subframe or one or more of LTE OFDM symbols in agiven subframe. LAA transmitters may transmit hybrid preamble in thisunused portions of the LTE frame structure. The unused portions of theframe structures are spaced such that the overall channel occupation ofthe LAA-LTE signal measured over a period of time doesn't exceed limitsimposed by regulatory requirements.

Similar to downlink transmission, the uplink transmission on an LAA-LTEchannel may last for one or more consecutive TTIs. The number ofconsecutive TTIs for which the UL will be occupied may be determined bythe eNB and signaled to the UEs. In some cases, the number ofconsecutive TTIs may be specified in a specification. In some cases,multiple UEs can transmit on a given TTI in UL. If all the UEstransmitting on a given UL TTI transmit a hybrid preamble, they maycreate cross talk and decoding failure at WLAN devices. In some cases,the eNB may direct one or a few of the scheduled UEs to transmit thehybrid preamble at the normal output power. In some cases, the normaloutput power level may be the maximum nominal allowed UL output power inthe band. Alternatively or in combination, the normal output level maybe signaled to the UE. In some cases, the normal output power level maybe the same output power level used for the transmission of the LTEsignal following the hybrid preamble. The other UEs may perform the CCAbut refrain from transmitting the hybrid preamble at the nominal outputpower. In some cases, some UEs may DTX (i.e., not transmit) the hybridpreamble. Alternatively or in combination, some UEs may transmit thehybrid preamble at a lower power. This approach may enable WLAN devicesto detect one or more hybrid preambles.

In some cases, the eNB may select the UEs to DTX the hybrid preamble orto transmit the hybrid preamble at a reduced power based on the UEs'locations within the cell. For example, the eNB may configure the UEsthat are spaced farthest apart in the cell to transmit the hybridpreamble at the normal power level. The eNB may configure other UEsaround these UEs to DTX the hybrid preamble or to transmit the hybridpreamble at a reduced power level. In some cases, the eNB may select theUEs that DTX the hybrid preamble or to transmit the hybrid preamble at areduced power level randomly, in a round-robin fashion, or based on aprevious battery status indication from the UE to the eNB. For example,the eNB may select a UE that has indicated a power-constrained status toDTX the hybrid preamble to save battery power.

In some implementations, the eNB may send an indication to the UEs toconfigure the UEs to transmit the hybrid preamble at a normal power orat a reduced power, or to DTX the hybrid preamble. In someimplementations, the eNB may transmit the indication with the UL grantsor as part of the UL grants, e.g., on a PDCCH channel. In someimplementations, the eNB may transmit the indication as part of RadioResource Control (RRC) configuration.

In some cases, the reduced output power level used for transmitting thehybrid preamble may be a preconfigured low output power level. Thereduced output power level may also be a power level which is lower thaneither the subsequent LTE signal transmission power level or the maximumnominal output power level by a preconfigured amount.

Turning to FIG. 17, the timing diagram 1700 includes a preamblestructure for a first UE 1770 and a second UE 1780. Both the first UE1770 and the second UE 1780 monitor the downlink and receive uplinkgrants. In the illustrated example, the first UE 1770 also receives anindication that configures the first UE 1770 to transmit the hybridpreamble at normal output power. The second UE 1780 receives anindication that configures the second UE 1780 to either DTX the preambleor transmit the hybrid preamble at a reduced power level. At a TTIboundary, the first UE 1770 performs CCA at the CCA period 1732 and thesecond UE 1780 performs CCA at the CCA period 1752. Upon the successfulCCAs, both UEs determine a starting time 1720 to access the channel. At1720, the first UE 1770 starts to transmit the hybrid preamble 1710 atnormal power, while the second UE 1780 starts to transmit the hybridpreamble 1750 at a reduced power or to DTX the hybrid preamble 1750. AtTTI boundary 1724, the first UE 1770 begins to transmit the LTE signal1706 and the second UE 1780 begins to transmit the LTE signal 1756.

FIG. 18 is an example timing diagram 1800 illustrating an Uplink (UL)hybrid preamble structure. The illustrated hybrid preamble may be usedin either a TDD system or an FDD system. In the illustrated example, aUE receives a UL grant as indicated by reference 1870, which grants a ULtransmission on the LAA-LTE channel at TTI boundary 1824. In theillustrated example, the preceding subframe, i.e., the subframe betweenthe previous TTI boundary 1822 and the TTI boundary 1824, is not usedfor LTE transmission. For example, an eNB may not schedule any ULtransmission on the LAA-LTE channel in the preceding subframe. In thiscase, the UE may perform CCA and transmit the hybrid preamble during thepreceding subframe (i.e. the subframe between TTI boundary 1822 and thenext TTI boundary 1824). In the illustrated example, the UE performs CCAduring the CCA period 1832, determines a starting time 1820 to transmiton the unlicensed carrier based on the CCA, transmits the hybridpreamble 1810 between the starting time 1820 and the TTI boundary 1824,and begins to transmit the LTE signal 1806 at TTI boundary 1824. In somecases, the CCA period 1832 may begin after the TTI boundary 1822.

FIG. 19 is an example timing diagram 1900 illustrating a hybrid preamblestructure in a Time Division Multiplex (TDD) operation. In theillustrated example, a UE receives a UL grant as indicated by reference1970, which grants a UL transmission on the LAA-LTE channel at TTIboundary 1924. In the illustrated example, the preceding subframe, i.e.,the subframe between the previous TTI boundary 1922 and the TTI boundary1924, is a special TDD subframe. The special TDD subframe includes aDwPTS 1972, a GP 1974, and an UpPTS 1976. In the illustrated example,the UE may perform CCA and transmit the hybrid preamble during the GP1974 and the UpPTS 1976. In the illustrated example, the UE performs CCAduring the CCA period 1932, determines a starting time 1920 to accessthe channel, transmits the hybrid preamble 1910 between the startingtime 1920 and the TTI boundary 1924, and begins to transmit the LTEsignal 1906 at TTI boundary 1924.

In some implementations, a special subframe format with a longer GPlength, e.g., format 0 specified in 3GPP TS 36.211, may be used toincrease the time for CCA. In some cases, the eNB may also DTX the DwPTS1972, so that CCA may start from the beginning of the TTI boundary 1922.In some instances, the system information may signal whether the DwPTS1972 of the special TDD subframe is DTXed or not. If the DwPTS 1972 isDTXed, then the UE may start CCA from the TTI boundary 1922. If theDwPTS 1972 is not DTXed, i.e., used for DL transmission, the UE maystart CCA from the GP 1974.

FIG. 20 is an example timing diagram illustrating a hybrid preamblestructure in an Uplink (UL) punctured LTE subframe. The illustratedhybrid preamble may be used in either a TDD system or an FDD system. Thetiming diagram 2000 includes an LTE subframe 2040. The timing diagram2000 also includes an idle period 2034, a CCA period 2032, and a hybridpreamble 2010. In addition, the timing diagram 2000 includes an LTEsignal 2006 that begins at a TTI boundary 2024. In the illustratedexample, similar to the DL operation described in FIG. 16, the LTEsubframe 2040 is punctured. In some cases, an eNB may determine whetherto leave the subframe preceding the scheduled transmission unoccupied orwhether to schedule a punctured LTE subframe in the subframe precedingthe scheduled transmission unoccupied. In some cases, the eNB may makethe determination based on the channel quality applicable to thepreceding subframe. The channel quality may be determined based onmeasurement reports or measurement of previous transmissions by thesame. If the channel quality is low, e.g., the path loss is high, theeNB may determine to leave the preceding subframe unscheduled, e.g., asillustrated in the example in FIG. 18.

In some cases, the eNB may signal to a UE, e.g., on the PDCCH channel,whether an LTE subframe is punctured. For example, the eNB may signal toUE to puncture the last OFDM symbol of the scheduled UL transmission.Alternatively, an eNB may signal to the UE to transmit a regular LTEsubframe without puncturing.

In some cases, the eNB may signal to a UE whether the subframe precedingthe scheduled transmission is unoccupied. In some cases, the eNB maysignal to the UE that the subframe preceding the scheduled transmissionis punctured.

In the illustrated example, the LTE subframe 2040 may be punctured. Insome cases, at least one OFDM symbol in the LTE subframe 2040 is usedfor CCA and hybrid preamble transmission and, therefore, is not used forLTE signal transmission. In these cases, the at least one OFDM symbol isan untransmitted OFDM symbol. In the illustrated example, the last OFDMsymbol is the untransmitted OFDM symbol in the LTE subframe 2040. Insome cases, the untransmitted OFDM symbol may be the first OFDM symbolin the LTE subframe. In some cases, more than one OFDM symbols may beuntransmitted and the untransmitted OFDM symbols may be located at anyposition within the LTE subframe. In the illustrated example, the idleperiod 2034 begins at the same time when the last OFDM symbol begins,followed by the CCA period 2032. In some cases, the duration of the idleperiod 2034 may be about 50 μs. In some cases, the CCA period 2032 maybe more than about 18 μs. The hybrid preamble 2010 begins at a startingtime 2020, when the channel is available for access based on CCA. Thehybrid preamble 2010 ends on the TTI boundary 2024, where the LTE signal2006 begins. In some implementations, e.g., in an LBE operation, theidle period 2034 may be omitted.

FIG. 21 is a flowchart illustrating an example method 2100 for sharing achannel in an LAA-LTE operation. The method 2100 may begin at block2102, where a starting time for transmission on an LAA-LTE channel isdetermined. In some cases, block 2102 involves at least one ofperforming CCA and determining that the channel is unoccupied. In someimplementations, the LAA-LTE channel is an unlicensed carrier that isconfigured for a licensed-assisted operation. In some cases, thedetermination may be performed by an evolved Node B (eNB) prior to aDownlink (DL) transmission by the eNB via CCA. Alternatively or incombination, the determination may be performed by a User Equipment (UE)prior to an Uplink (UL) transmission by the UE.

At block 2104, a length of a hybrid preamble is determined based on thestarting time and a predetermined transmission time boundary. In somecases, the predetermined transmission time boundary is a TransmissionTime Interval (TTI) boundary. In some cases, at block 2110, the hybridpreamble includes a Wireless Local Area Network (WLAN) CompatibleSection (WCS) that indicates a length of the LTE signal. In these cases,the length of the hybrid preamble is equal to the length of a WirelessLocal Area Network (WLAN) Compatible Section (WCS). In some cases, atblock 2112, the hybrid preamble includes a Wireless Local Area Network(WLAN) Compatible Section (WCS) and a Variable Length Section (VLS). TheWCS may indicate a length of the LTE signal. The VLS may have a lengththat is determined based on a difference between the length of thehybrid preamble and a length of the WCS. In these cases, the length ofthe hybrid preamble is larger than the length of a WCS. In some cases,at block 2114, the hybrid preamble includes a Variable Length Section(VLS) having a length that is determined based on the length of thehybrid preamble. In these cases, the length of the hybrid preamble issmaller than the length of a WCS.

In some cases, the hybrid preamble contains only a VLS sectionregardless of the length of the hybrid preamble.

At block 2120, subsequent to the determination of the length of thehybrid preamble, the hybrid preamble having the determined length istransmitted. In some cases, the transmission may be a DL transmissionthat is transmitted by the eNB. Alternatively or in combination, thetransmission may be a UL transmission that is transmitted by the UE. Insome cases, prior to transmitting the hybrid preamble, a transmissiongrant that grants a transmission of the LTE signal and an indicationthat indicates a transmission power level of the hybrid preamble may bereceived. The indication may indicate that the hybrid preamble istransmitted at a normal power level or at a reduced power level. Inthese cases, the hybrid preamble may be transmitted in accordance withthe indication.

In some implementations, the hybrid preamble is transmitted in a firstsubframe prior to the predetermined transmission time boundary and theLTE signal is transmitted in a second subframe after the predeterminedtransmission time boundary. In some cases, the first subframe includesan LTE signal adapted to occupy only a subset of symbols in the firstsubframe. In these cases, the hybrid preamble is transmitted during atime period corresponding to symbols not within the subset.

At block 2130, subsequent to the hybrid preamble, a Long Term Evolution(LTE) signal may be transmitted. In some cases, at block 2140, atransmission grant that grants a transmission of a second LTE signal isreceived. The transmission grant may include an indication to transmitthe second LTE signal without a preceding hybrid preamble. At block2142, in response to the indication, the second LTE signal istransmitted without a preceding hybrid preamble.

FIG. 22 is a block diagram illustrating an example user equipment (UE)device 2200. The illustrated device 2200 includes a processing unit2202, a computer-readable storage medium 2204 (for example, ROM or flashmemory), a wireless communication subsystem 2206, a user interface 2208,and an I/O interface 2210.

The processing unit 2202 can include one or more processing components(alternatively referred to as “processors” or “central processing units”(CPUs)) configured to execute instructions related to one or more of theprocesses, steps, or actions described herein in connection with one ormore of the implementations disclosed herein. In some implementations,the processing unit 2202 may be configured to generate controlinformation, such as a measurement report, or respond to receivedinformation, such as control information from a network node. Theprocessing unit 2202 may also be configured to make an Radio ResourceManagement (RRM) decision such as cell selection/reselection informationor trigger a measurement report. The processing unit 2202 can alsoinclude other auxiliary components, such as random access memory (RAM)and read-only memory (ROM). The computer-readable storage medium 2204can store an operating system (OS) of the device 2200 and various othercomputer-executable instructions, logic or software programs forperforming one or more of the processes, steps, or actions describedabove.

The wireless communication subsystem 2206 may be configured to providewireless communication for voice, data and/or control informationprovided by the processing unit 2202. The wireless communicationsubsystem 2206 can include, for example, one or more antennas, areceiver, a transmitter, a local oscillator, a mixer, and a digitalsignal processing (DSP) unit. In some implementations, the subsystem2206 can support multiple input multiple output (MIMO) transmissions. Insome implementations, the receiver in the wireless communicationsubsystems 2206 can be an advance receiver or a baseline receiver. Tworeceivers can be implemented with identical, similar, or differentreceiver processing algorithms.

The user interface 2208 can include, for example, one or more of ascreen or touch screen (for example, a liquid crystal display (LCD), alight emitting display (LED), an organic light emitting display (OLED),a micro-electromechanical system (MEMS) display), a keyboard or keypad,a trackball, a speaker, and a microphone. The I/O interface 2210 caninclude, for example, a universal serial bus (USB) interface. Variousother components can also be included in the device 2200. A number ofembodiments of the invention have been described. Nevertheless, it willbe understood that various modifications may be made. Accordingly, otherembodiments are within the scope of the following claims.

FIG. 23 is a block diagram illustrating an example eNB 2300. Theillustrated eNB 2300 includes a processing module 2302, a wiredcommunication subsystem 2304, and a wireless communication subsystem2306. The wireless communication subsystem 2306 can receive data trafficand control traffic from the UE. In some implementations, the wirelesscommunication subsystem 2306 may include a receiver and a transmitter.The wired communication subsystem 2304 can be configured to transmit andreceive control information between other access node devices viabackhaul connections. The processing module 2302 can include one or moreprocessing components (alternatively referred to as “processors” or“central processing units” (CPUs)) capable of executing instructionsrelated to one or more of the processes, steps, or actions describedabove in connection with one or more of the implementations disclosedherein. The processing module 2302 can also include other auxiliarycomponents, such as random access memory (RAM), read-only memory (ROM),secondary storage (for example, a hard disk drive or flash memory). Insome implementations, the processing module 2302 may be configured togenerate control information or respond to received information such asa measurement report transmitted from a UE. The processing module 2302may also be configured to make an RRM decision based at least in part onthe information transmitted from the UE, such as cellselection/reselection information or the measurement report. Theprocessing module 2302 can execute certain instructions and commands toprovide wireless or wired communication, using the wired communicationsubsystem 2304 or a wireless communication subsystem 2306. Various othercomponents can also be included in the eNB 2300.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be employed. Moreover, the separation of various system componentsin the implementation descried above should not be understood asrequiring such separation in all implementations, and it should beunderstood that the described program components and systems cangenerally be integrated together in a signal software product orpackaged into multiple software products.

Also, techniques, systems, subsystems, and methods described andillustrated in the various implementations as discrete or separate maybe combined or integrated with other systems, modules, techniques, ormethods. Other items shown or discussed as coupled or directly coupledor communicating with each other may be indirectly coupled orcommunicating through some interface, device, or intermediate component,whether electrically, mechanically, or otherwise. Other examples ofchanges, substitutions, and alterations are ascertainable by one skilledin the art and could be made.

While the above detailed description has shown, described, and pointedout the fundamental novel features of the disclosure as applied tovarious implementations, it will be understood that various omissions,substitutions, and changes in the form and details of the systemillustrated may be made by those skilled in the art. In addition, theorder of method steps are not implied by the order they appear in theclaims.

What is claimed is: 1-39. (canceled)
 40. A method for transmitting on aLicensed-Assisted Access in Long Term Evolution (LAA-LTE) channel,comprising: determining a starting time for transmission on the LAA-LTEchannel; determining a length of a preamble based on the starting timeand based on a predetermined transmission time boundary; transmitting,by an evolved Node B (eNB) and subsequent to determining the length ofthe preamble, the preamble having the determined length, wherein thepreamble is transmitted in a first subframe that is prior to thepredetermined transmission time boundary, and the preamble istransmitted during a time period corresponding to a subset of fewer thanall orthogonal frequency-division multiplexing (OFDM) symbols within thefirst subframe; transmitting, subsequent to transmitting the preamble, aLong Term Evolution (LTE) signal, wherein the LTE signal is transmittedin a second subframe different than the first subframe, the secondsubframe being after the predetermined transmission time boundary;transmitting, to a user equipment (UE), a transmission grant that grantsa transmission of a second LTE signal, wherein the second LTE signal istransmitted without a preceding preamble; and subsequent to transmittingthe transmission grant, receiving, from the UE, the second LTE signalwithout a preceding preamble.
 41. The method of claim 40, wherein thepredetermined transmission time boundary is a Transmission Time Interval(TTI) boundary.
 42. The method of claim 40, wherein the preamblecomprises a Wireless Local Area Network (WLAN) Compatible Section (WCS)that indicates a length of the LTE signal.
 43. The method of claim 42,wherein the length of the preamble is equal to a duration of the WCS.44. The method of claim 40, wherein the preamble comprises a WirelessLocal Area Network (WLAN) Compatible Section (WCS) and a Variable LengthSection (VLS), and wherein the WCS indicates a length of the LTE signaland the VLS has a length that is determined based on a differencebetween the length of the preamble and a length of the WCS.
 45. Themethod of claim 44, wherein the length of the preamble is larger thanthe length of the WCS.
 46. The method of claim 40, wherein the preamblecomprises a Variable Length Section (VLS) having a length that isdetermined based on the length of the preamble.
 47. The method of claim40, wherein the LAA-LTE channel is an unlicensed carrier that isconfigured for a Licensed-Assisted operation.
 48. A base station,comprising: a memory; and at least one hardware processorcommunicatively coupled with the memory and configured to: determine astarting time for transmission on a Licensed-Assisted Access in LongTerm Evolution (LAA-LTE) channel; determine a length of a preamble basedon the starting time and based on a predetermined transmission timeboundary; transmit, subsequent to determination of the length of thepreamble, the preamble having the determined length, wherein thepreamble is transmitted in a first subframe that is prior to thepredetermined transmission time boundary, and the preamble istransmitted during a time period corresponding to a subset of fewer thanall orthogonal frequency-division multiplexing (OFDM) symbols within thefirst subframe; transmit, subsequent to transmission of the preamble, aLong Term Evolution (LTE) signal, wherein the LTE signal is transmittedin a second subframe different than the first subframe, the secondsubframe being after the predetermined transmission time boundary;transmit, to a user equipment (UE), a transmission grant that grants atransmission of a second LTE signal, wherein the second LTE signal istransmitted without a preceding preamble; and subsequent to transmissionof the transmission grant, receiving, from the UE, the second LTE signalwithout a preceding preamble.
 49. The base station of claim 48, whereinthe predetermined transmission time boundary is a Transmission TimeInterval (TTI) boundary.
 50. The base station of claim 48, wherein thepreamble comprises a Wireless Local Area Network (WLAN) CompatibleSection (WCS) that indicates a length of the LTE signal, and wherein thelength of the preamble is equal to a duration of the WCS.
 51. The basestation of claim 48, wherein the preamble comprises a Wireless LocalArea Network (WLAN) Compatible Section (WCS) and a Variable LengthSection (VLS), and wherein the WCS indicates a length of the LTE signaland the VLS has a length that is determined based on a differencebetween the length of the preamble and a length of the WCS, and whereinthe length of the preamble is larger than the length of the WCS.
 52. Thebase station of claim 48, wherein the preamble comprises a VariableLength Section (VLS) having a length that is determined based on thelength of the preamble.
 53. The base station of claim 48, wherein theLAA-LTE channel is an unlicensed carrier that is configured for aLicensed-Assisted operation.
 54. A non-transitory computer-readablemedium containing instructions which, when executed, cause a computingdevice to perform operations comprising: determining a starting time fortransmission on the LAA-LTE channel; determining a length of a preamblebased on the starting time and based on a predetermined transmissiontime boundary; transmitting, by an evolved Node B (eNB) and subsequentto determining the length of the preamble, the preamble having thedetermined length, wherein the preamble is transmitted in a firstsubframe that is prior to the predetermined transmission time boundary,and the preamble is transmitted during a time period corresponding to asubset of fewer than all orthogonal frequency-division multiplexing(OFDM) symbols within the first subframe; transmitting, subsequent totransmitting the preamble, a Long Term Evolution (LTE) signal, whereinthe LTE signal is transmitted in a second subframe different than thefirst subframe, the second subframe being after the predeterminedtransmission time boundary; transmitting, to a user equipment (UE), atransmission grant that grants a transmission of a second LTE signal,wherein the second LTE signal is transmitted without a precedingpreamble; and subsequent to transmitting the transmission grant,receiving, from the UE, the second LTE signal without a precedingpreamble.
 55. The non-transitory computer-readable medium of claim 54,wherein the predetermined transmission time boundary is a TransmissionTime Interval (TTI) boundary.
 56. The non-transitory computer-readablemedium of claim 54, wherein the preamble comprises a Wireless Local AreaNetwork (WLAN) Compatible Section (WCS) that indicates a length of theLTE signal, and wherein the length of the preamble is equal to aduration of the WCS.
 57. The non-transitory computer-readable medium ofclaim 54, wherein the preamble comprises a Wireless Local Area Network(WLAN) Compatible Section (WCS) and a Variable Length Section (VLS), andwherein the WCS indicates a length of the LTE signal and the VLS has alength that is determined based on a difference between the length ofthe preamble and a length of the WCS, and wherein the length of thepreamble is larger than the length of the WCS.
 58. The non-transitorycomputer-readable medium of claim 54, wherein the preamble comprises aVariable Length Section (VLS) having a length that is determined basedon the length of the preamble.
 59. The non-transitory computer-readablemedium of claim 54, wherein the LAA-LTE channel is an unlicensed carrierthat is configured for a Licensed-Assisted operation.